It is the general practice in many analyzers to use disposable tips on permanent dispensing probes, so that each new sample is aspirated into, and dispensed out of, a new tip. Hence, cross-contamination between samples is avoided.
It is also customary to provide such tips premade with specific, fairly complex shapes, as shown for example as the "rocket" shape in U.S. Pat. No. 4,347,875, to provide for certain dispensing functions. Although such tips work admirably, they have a few drawbacks: they are somewhat expensive to mold, and because they are supplied as discrete parts, they are not easily and quickly added to the analyzer and mated with the dispensing probe. Delays in the later are not significant, except if a high-speed analyzer is desired with maximum throughput.
On the other hand, it is old in the art to provide a very inexpensive pipette which comprises only a continuous cylindrical plastic tubing, of considerable length, and to compress a significant part of the length between two plates to a) aspirate, and then b) dispense liquid sucked into the portion not compressed. When dispensing is complete, the tubing is simply advanced by counter-rotating rollers until a knife can cut off the used portion, and a new portion of the continuous tubing is then presented for use. Examples are disclosed in U.S. Pat. No. 3,736,099. Although such an approach solves the problem of expense, it relies on exterior plates to compress the tube to generate aspiration and dispensing pressure. Such a mechanism is not as accurate as the pumps that have been conventionally used with the permanent probes that mount the tips described in the '875 patent. That is, the collapsing of the tubing to generate pressures, can be variable. Also, this approach is limited to the use of resiliant tubes and thus excludes the use of rigid tubes. Accurate dispensing has become very important, in this age of quantitative assays conducted using, e.g., dried slide test elements, given that very small total volumes of liquid are used (10 .mu.L). An error of 5 .mu.L, though not large when pin-pricking a linger for home-testing of blood, makes a 50% difference if the total optimum volume is 10 .mu.L.
Hence, the continuous tubing approach has never achieved a significant commercial status as a disposable pipette tip, notwithstanding its availability in the public literature since 1973.
Thus there has been a need for a method and apparatus for making a disposable tip, that is as inexpensive as a continuous cylindrical tubing, but which has the accuracy of the more expensively molded "rocket" tips.